The invention is based on an injection timing adjuster for internal combustion engines.
An injection timing adjuster of this type is already known from German Patent 33 39 009. Here, via intermediate elements and transmission elements located on them and via an eccentric adjusting mechanism, the reciprocating motion of adjusting pistons guided in a piston holder is converted into a mutual rotation of two coaxial shafts, namely a drive shaft and a driven shaft. Two adjusting pistons at a time are disposed parallel to one another on one side of the adjuster, in a plane at right angles to the longitudinal axis of the adjuster. Coupling pins, each of which protrudes into a transverse bore in one of the adjusting pistons and is firmly joined to one of the intermediate elements, are provided as the transmission elements between the adjusting pistons and the intermediate elements. The longitudinal axes of the coupling pins extend vertically to the longitudinal axis of the adjuster and vertically to the longitudinal axes of the adjusting and the intermediate elements. The longitudinal axes of the coupling pins extend vertically to the longitudinal axis of the adjuster and vertically to the longitudinal axes of the adjusting piston. Because of the eccentric action of the adjusting mechanism, upon an adjustment of the two shafts relative to one another, the piston holder is rotated on its guide portion, and the forces necessary for rotating the piston holder are transmitted to the piston holder both by the coupling pins protruding into the adjusting pistons and by the adjusting pistons themselves. The adjusting pistons are additionally stressed by the resultant shear forces and can seize in their guides in the piston holder and wear down.
Each of the coupling pins protrudes into a central bore of the associated adjusting piston, because it is for instance not possible to connect two parallel adjusting pistons to one common coupling pin; otherwise the adjusting pistons, with their lower edges, would open into slits in the piston holder necessary for the passage of the coupling pins. Accordingly, the coupling pins can be connected to the intermediate elements only at one end, and because of the slight wall thickness of the intermediate elements, only short connecting lengths are possible. The one-ended support of the coupling pins entails the risk that they may bend or become separated from the connecting bore or tilt, which would cause the adjusting pistons to seize. Upon an adjustment, the intermediate elements move radially outward or inward and are radially guided only via the coupling pins and the adjusting pistons. Because of play and hence tilting of the coupling pins in the adjusting pistons, it is possible that the intermediate elements may seize in the course of a radial motion.